The big picture: Community ecology



  • Community:
    • small scale: decomposers on a fallen log
    • large scale: flowers + pollinators in a national park


  • Interactions can help, harm or have no effect


  • Outcome of interactions determine which species are present


  • Sum of interactions determine how an ecosystem functions

Inter-specific Competition (-/-)




  • Individuals sharing space will compete for resources
    • limits fitness for each species


  • Resources can mean man things:
    • prey items, water, nutrients, space


  • Competitive exclusion:
    • local extinction
    • rare in nature

Natural selection favors those that do not compete



  • Ecological niche:
    • temperature, time active, prey choice, nest sites
    • competition occurs for these resources


  • Natural selection reduces overlap between niches!
    • resource partitioning: division of limited resources
    • How?


  • Resource partitioning allows for coexistence
    • partial niche overlap
    • why competitive exclusion is rare!

Resource partitioning in Anolis lizards


There is serious DRAMA in the animal kingdom!!!





  • Review: all animals are heterotrophic….


  • All animals must eat, which means that most organisms are at the risk of being eaten


  • Exploitation: species feeding interactions (+/-)
    • predation, herbivory & parasitism
    • drama causes evolution!

Predation (+/-)





  • One species (predator) kills and eats other (prey)
    • does not have to be animal on animal


  • Lot of feeding adaptation in the animal world
    • reproductive success depends on feeding


  • Fangs, claws, echo-location, venom, etc. etc. etc.

Predation (+/-)




  • Not getting eaten is just as important as eating
    • powerful driver of natural selection


  • Behavioral adaptations
    • hiding, fleeing, herding
    • active self defense less common


  • Morphological adaptations
    • spines, odors, toxin accumulation
    • mimicry and camouflage

Defenses → Co-evolutionary arms race


https://youtube/w-K_YtWqMro


Herbivory (+/-)



  • Organism (herbivore) eats part of plant or alga
    • harms the plant


  • Herbivores are large & small, terrestrial & aquatic


  • Like predators, many special adaptations
    • chemical sensors to identify toxins
    • specialized teeth or digestive systems


  • Review: Plants don’t move
    • just as many defensive adaptations
    • thorns, toxins, etc.

Parasitism (+/-)





  • Organism (parasite) gets nourishment from host
    • host harmed in process
    • ~1/3 of all species are parasites!!


  • Parasites live inside or outside body of host
    • tapeworms → ticks


  • Parasite usually have complex life cycles

Species interactions are not all bad!






  • Positive interactions occur where one at least one species benefits and their other is not harmed


  • Positive interactions affect diversity of ecological communities


  • Mutualisms and commensalism are the most common

Mutualism (+/+)




  • Mutualism occur when both species benefit from the interaction
    • common in nature


  • Often, the 2 species depend on each other for survival/reproduction
    • plants + insects = pollination + food


  • Usually still a cost, but benefit > costs
    • carbon - nitrogen trade-off between plants and fungi

Commensalism (+/0)





  • Commensalisms are interactions where one benefits but doesn’t harm/help the other
    • also common in nature


  • Some biologists argue that any close interaction between two organisms is unlikely to be completely neutral for either party
    • especially over time

Trophic Structure




  • Structure and dynamics of a community depend on feeding relationships


  • Energy is transferred upward
    • plants → consumers
    • transfer is wasteful


  • Trophic level:
    • organisms in a community share a trophic level

Trophic Structure




  • Structure and dynamics of a community depend on feeding relationships


  • Energy is transferred upward
    • plants → consumers
    • transfer is wasteful


  • Exists in terrestrial and aquatic systems
    • What happens if a species goes extinct?

Food webs are multi-dimensional


Some species in a community are more impactful than others





  • Dominant species:
    • better @ obtaining resources
    • defense wins championships


  • Keystone Species:


  • Ecosystem engineers: